I wanted to post some Slaty-backed Gulls, but haven't come across all that many yet so far this year. The first reason for this is that my coastal site (a sandbar) has become popular with fishermen and fewer and fewer gulls are willing to settle on it. The second is that it is has always been somewhat 'hit and miss' anyway, with often nothing there at all. This year seems to be a bit of a poor one.
I did get one striking first-winter earlier in the month, though, a very bleached affair. Slaty-backed Gulls seem to be very prone to bleaching, and most 'white' things turning up at this time of year turn out to be Slaty-backeds. Other useful characteristics are the big eye of first-winters, the thick, droopy cigar-shaped bill, the dark belly patch (always the last thing to go), and lack of patterning in the tail (solid, whether bleached or not).
Additionally, Slaty-backed Gulls when stood adopt a wide-legged stance. Coupled with their shortish rear ends, this gives them a look something almost akin to a Northern Shoveler!
Attached: First-winter Slaty-backed Gull (ID'd by broad head, dark belly patch, excessive bleaching, and solid tail band).